The present invention relates to deflation proof tires and more particularly concerns a solid-filled tire having improved characteristics. Solid rubber tires and solid-filled tires find continued use in wheeled vehicles, particularly in those units adapted for relatively low speeds and support of heavy loads. The solid-filled tire, of course, has the major advantage of increased wear and proof against puncture and deflation caused by various types of road hazards. Inflated or pneumatic tires on the other hand, have many advantages including those relating to improved ride characteristics.
Operation of the inflated tire depends primarily upon stresses imposed upon the tire casing. In general, proper inflation maintains the casing under substantially evenly distributed pressures or tension. Upon deflation, due to puncture or other hazards, the inflated tire can no longer function properly. In the light of this problem, many attempts have been made to replace the inflation fluid by non-compressible or elastic solid material such as sponge rubber or the like. However, such tires either have excessive stiffness or do not provide required stress distribution.
Lack of proper stress distribution under load is a major problem of filled tires. Thus, under high torque conditions, the filled tire will often tend to slip on the wheel rim. This is due to the fact that pressure applied to, by and throughout the filled tire is not uniform throughout the tire as it is with the pneumatic tire. In the pneumatic tire, as weight is applied to the vehicle, the additional pressure resulting from compression from the tire distributes itself equally throughout the tire and applies equal pressure to force the tire bead against the rim of the wheel thereby increasing the resistance to slippage of the casing relative to the wheel rim.
In the solid or solid filled tire, this slippage resistance is greatly decreased. Added pressure, as a result of load on the vehicle, results in localized compression of the tire and fill material at the lower part of the wheel, that is, between the wheel axis and the point of contact with the ground. Furthermore, this pressure is not distributed evenly throughout the tire but actually tends to raise the upper part of the tire relative to the wheel itself. This has the effect of relieving the pressure and thereby the frictional forces between the upper portion of the tire and the wheel, wherefore the tendancy to slip in the presence of high torque is increased.
Still another disadvantage of the solid or filled tire is its tendancy to transmit road shocks directly to the wheel and thus to the entire suspension system when the solid tire or fill material reaches a stressed condition of decreased compressibility.
An attempt to solve some of these problems is shown in the patent to Fischman U.S. Pat. No. 3,205,928 wherein a solid rubber tire is mounted upon a wheel having at least one removably secured flange and an inflatable tube to obtain a desired gripping relation. However, this solid tire, just as other solid tires, requires special tire construction and also special wheel construction. Use of such an arrangement requires total replacement of present tires and wheels, whereas it is highly desirable to provide protection against deflation in existing, conventional tires and wheel assemblies.
Accordingly, it is an object of the present invention to provide a deflation-proof tire that is substantially free of disadvantages inherent in solid and solid-filled tires previously known.